Change the date or time format
Click the cell (the intersection of a row and column that can contain text or numbers), or select (move the plus sign to the beginning of a cell, click and hold down the mouse button while moving the plus sign over the cell or cells you want, and then release the mouse button) the group of cells, that contains the date or time you want to change.
On the Format menu, click Number.
Under Format, click Date or Time.
Under Options, click the format you want for the date or time.
Click OK.
Note If you decide you don't like the new format, immediately click Undo Format on the Edit menu.